1. Field of the Invention
The present invention relates to a power driven screwdriver, and particularly to a power driven screwdriver having a device for preventing rotation of a spindle during fitting operation of a screw on a driver bit mounted on the spindle.
2. Description of the Prior Art
In a power driven screwdriver, for driving a screw by the power driven screwdriver, the screw is fitted on a driver bit and is driven by rotating the driver bit through a spindle. To ensure safe fitting operation of the screw on the driver bit, it has been proposed to provide a device for preventing rotation of the spindle during such fitting operation of the screw.
The spindle is driven by a motor through a clutch mechanism such as a claw clutch. The spindle is slidably movable in an axial direction between two positions, one for disengagement of the clutch mechanism and the other for engagement of the clutch mechanism. A spring is provided to normally bias the spindle in a direction to the position for disengagement of the clutch mechanism. When the clutch mechanism has been disengaged, the spindle which has been driven by the motor through the clutch mechanism tends to continuously rotate by a frictional force of the spring against the spindle.
Thus, the device for preventing rotation of the spindle is provided in the screwdriver and conventionally, the device includes an O-ring which is Positioned coaxially with the spindle and which may contact a part of the spindle with the aid of the biasing force of the spring when the clutch mechanism has been disengaged. The O-ring provides a frictional force against the rotation of the spindle.
However, the conventional device for preventing rotation of the spindle utilizing the O-ring cannot be reliably operated because of variations in performance or quality in manufacturing O-rings.